The present invention relates to a method of improving the permeability of a hydrocarbon bearing formation and more particularly relates to an electrolinking method for improving the permeability of a formation such as a coal seam in which an in situ gasification operation is to be carried out.
Due to the nature and position of certain hydrocarbon bearing formations (e.g., deep lying coal seams), it is sometimes desirable to recover the hydrocarbons by gasifying the hydrocarbons in situ and producing the resulting products. Typically, this is done by circulating a gasifying agent (e.g., heated gas) between an injection well and a production well which have been completed into the formation. Unfortunately, however, many of these formations are relatively impermeable and must be treated in some way to establish the necessary fluid communication between wells before a successful in situ gasification operation can be performed.
Several methods are known for improving permeability between wells in such hydrocarbon formations, one of which is commonly referred to as "electrolinking." As explained in "A Current Appraisal of Underground Coal Gasification," Arthur D. Little, Inc., Apr. 17, 1972 (PB-209, 274) pp. 21 et sec., (distributed by National Technical Information Service of U.S. Department of Commerce), electrolinking is a process wherein electrodes are installed within a formation such as a coal seam at a given spacing. Electric current is passed between the electrodes which carbonizes the coal along the path taken by the electricity and this, in turn, provides a path of increased permeability within the formation through which gases may flow.
In establishing electrolinked paths through a formation, normally "point " sources and sinks are used which provide a substantially small path in relation to the thickness of the formation. Since it is desirable to increase the permeability in as much of the formation as possible, the more individual paths established between wells for the flow of current, the better improvement will be in the overall permeability of the formation.